The present invention relates generally to planar antennas, and more particularly, to a planar antenna radiating structure having a quasi-scan, frequency-independent driving-point impedance.
Examples of planar radiating elements include printed patches and slot radiators. Recent innovations in patch arrays have resulted in significant increases in operating bandwidth. However, broadband patch designs are typically limited to only about twenty to thirty percent bandwidth. Further, the circuit losses of patch arrays seriously limit their efficiency, especially in electrically large arrays and/or arrays operating at millimeter-wave frequencies. Slotted waveguide arrays are planar and have low losses. However, the operating bandwidth is typically limited to less than fifteen percent.
Both types of radiators are essentially resonant structures, exhibiting typical "high-Q" characteristics which limit their ultimate frequency bandwidth due to significant reactive components. In addition, both structures exhibit strong scan-dependent driving-point impedance characteristics due to strong, ill-behaved mutual coupling and potential surface-wave phenomena.
Accordingly, it is an objective of the present invention to provide for an improved planar antenna radiating structure having a quasi-scan, frequency-independent driving-point impedance.